Automatic feed for boring bars



June 28, 1938. c. T. ROTTLER 2,122,072

AUTOMATIC FEED FOR BORING BARS Filed March 25, 1936 3 Sheets-Sheet l Fig. 7

Ema who e Clarence T. Rodlen gmzgwm June 28, 1938.

I AUTOMATIC FEED FOR BORING BARS Filed March 25, 1956 3 Sheets-Sheet 2 Clarence T. Bauer c. T. ROTTLER 2,122,072

June 28, 1938. c, ROTTLER 2,122,072

AUTOMATIC FEED FOR BORING BARS File d March 25, 1936 3 Sheets-Sheet 3 gwucnto'n Clarence T. Ro-Pcler Patented June 28, 1938 UNITED STATES PATENT OFFICE 14 Claims.

My invention relates to boring bars, that is, machines usually employed in reboring the cylinders of internal combustion engines, of the general type illustrated in my Patent No.

: It is particularly an object of the present invention to provide means controlling movement of the boring bar whereby it may be fed slowly downward, moved upward, or moved downward rapl idly, and whereby all such movements may be either necessarily under control of the operator, or under control of elements which will automatically stop or reverse the movement of the boring bar upon completion of a predetermined l amount of such movement, to the end that the operation of the boring bar may be made substantially automatic. Y

The term feeding, as herein used, shall be taken to mean movement, whether during cutting operation of the boring bars tool bit, or

otherwise.

It is a further object to provide automatic control mechanism for'slow downward feed which maybe readily adjustable in accordance with the depth of the cylinder upon which the boring bar is operating.

It is a further object to provide interlocking mechanism and such arrangement of the several controls that one control only may function at a v time,'to the end that there cannot be interference I between two different drive mechanisms, each driven from the same source of power.

It is a further object to devise control and'feed mechanism of this general type which can be thrown into a neutral ora nonoperative position atany time, as for example, in an emergency, to stop *all feeding movement of the boring bar.

More specifically, it is an object to devise control mechanism which may be positioned in a given position to accomplish downward feed of the'boring bar, and adjustable automatic reversing mechanism cooperating therewith which, at thepredetermine'd limit of downward movement'of the boring bar, will automatically reverse the control mechanismto commence upward movement of the boringbar, and further, to devise means which upon the completion of the up- Wardmovement' of the boring bar will automatically throw the control mechanism into neutral position, thereby stopping movement of. the boring bar, and holding it in its uppermost position,

It is also an object'to provide latching mechanism to hold such controls in either position, which, latch mechanism is automatically disengagged upon the boring bar reaching either the upward or downward limit of its movement, in

' order that reversal thereof, or the throwing of the same into neutral position, may be accomplished.

It is a further object to simplify the driving 6 mechanism of such a boring bar, and to condense it into the smallest practicable space, to the end that the boring bar may be neat and compact, and of weight sufficiently low that it may readily be moved from place to place, as 10" required.

It is a further object to devise an accurate boring bar, yet one wherein the component parts need not be finished or fitted with extreme accuracy, thereby lessening the cost of production 6 and the liability to get out of order.

It is an object to devise mechanism which will insure rotation of the screw and nut at identical speeds, when the control mechanism is in neutral position, so that there will be no tend- 20 ency for the boring bar to move up and down, when it is intended that it shall stand still. This makes possible the use of a tool-lapping arrangement disclosed and claimed in my copending application Serial No. 70,858, filed March 25, 1936. 25

These and other objects will be better understood as the present specification progresses.

My invention comprises the novel boring bar and the novel arrangement and combination of the parts thereof, as shown in the accompanying 30, drawings, described in this specification, and as will be more particularly pointed out and defined by the claims which terminate the same.

In the accompanying drawings I have shown my invention incorporated in a preferred form of 35 boring bar, and in a form now preferred by me, it being understood, however, that such changes may be made in the form, proportion and arrangement of the parts, within this disclosure, as may be included within the claims. 40

Figure 1 is an elevation of the boring bar, parts being broken away, and the cylinder block being shown fragmentarily and in section.

Figure 2 is an elevation, with parts broken away, of the upper end of the boring bar, and 45 Figure 3 is a section through the same substantially on the line 3-3 of Figure 2.

Figures 4, 5 and 6 are transverse vertical sections through the head of the boring bar, taken on the respective lines 44, 55, and 6--6 of 50 Figure 2, Figures 5 and 6, however, showing parts in a different position than that illustrated in Figure 2.

Figure 7 is a detail section through the control handle and latching means. 55

The hollow boring bar 9 is vertically slidable in suitable bearings within a base 99, and on its lower end is rotatable a cutter head 9| carrying the fly cutter 92. Projectable fingers 93, movable inwardly and outwardly at will, are also provided on the cutter head, and a rod 94, extending axially through the axial bore of the boring bar 9 and terminating in a handle 94, is rotatable to control projection and retraction of the fingers 93, and is vertically movable to control projection and retraction of the tool 92. A handle or lever 99 enables manual lifting of the rod 94 when required.

A motor 95 is preferably mounted upon the base, and extending upwardly from and geared to the motor, to be rotated thereby, is a shaft 96. This is journaled in the base and extends through the head 91, carried by the upper end'of the boring bar 9 and constituting a gear casing. The shaft 96 is screw threaded (right-handed, and rotating in the direction of the arrow A in Figure 5, as shown) and terminates at its upper end in an enlarged handle 96'. These arrangements (other than the use of a screw which rotates in the indicated direction, with relation to the direction of its thread) are not part of the present invention, but known in the prior art, and no further detailed description thereof is deemed nec essary, nor is it deemed necessary to describe the anchor 4 in detail, this comprising a portion which is supported within a cylinder other than the one being worked upon by the cutter 92, and which is secured to the base 90 to hold it down upon the top of the cylinder block.

The drivearrangement for the boring bar is somewhat different from that shown in my patent referred to above, and will be described for better understanding of the invention. The screw threaded shaft 96 is longitudinally grooved as indicated at 96" to receive a key 19 whereby a gear 1, which constitutes the driving gear, is secured to rotate with the shaft 96. Loosely mounted upon a sleeve 1 integral with the gear 1 is a gear 10, which has a slightly different number of teeth than the gear 1, preferably one more tooth, so that the two constitute differential gears. Both these gears mesh with a gear H, and the gear 10 is provided with clutch elements 12 with which may be meshed complemental clutch elements 13 upon a slidable clutch sleeve 14. This sleeve 14 is keyed at 75 to a nut 16 threaded upon the threaded shaft 96.

The slidable clutch sleeve M is further provided with gear teeth 78, with which is meshed a gear 6. With the driving gear 1 is meshed a smaller gear 60, loose upon a stub shaft 6| and provided with clutch elements 62 capable of engaging with complemental clutch elements 63 upon the large gear 6. A spring pressed plunger 64 (see Figure 2), received in an axial bore'of the stub shaft 6|, normally holds the complemental clutch elements 62 and 63 out of engagement, but the two may be engaged by a yoke 58, acting through a lever 51 fulcrumed at 56 topress downward the pin 65, guided at 66 in the head 91, when the yoke 58 is raised (compare Figures 2 and 6), such raising of the yoke 58 being accomplished by raising the control handle 52, as will be later described in detail. As a result of engaging the clutch elements 62 and 63, the head 9'|-and the boring bar are moved rapidly upward.

Control of the engagement and disengagement of clutch elements 73 and 12, and of clutch elements 63 with62, may be accomplishedby a rock shaft 5 (see Figures 2, 3, 4, and 6), which is pivotally received in the interior of the head 91, and which may be rocked by the control handle 52. Fingers 50 on this rock shaft engage a collar 94 on the rod 94 to raise it when the rock shaft 5 is suitably rocked, thus to effect or permit withdrawal of the tool 92 inwardly of the cutter head 9|. Another finger 5| engages in a groove 14' of the member 14, whereby to control movement of the latter. When the control handle 52 is shifted upwardly the clutch elements 13 are disengaged from clutch elements 12, and when said handle is shifted downwardly T3 is engaged with 12. Upward movement of the control handle 52 engages the clutch elements 63 and 62, and downward movement permits their disengagement, hence there can never be a tendency for downward slow feedlby engagement of 13 and 12) at the same time as fast upward feed (by engagement of 63 and 62).

If it is'desired to effect downward feed of the boring bar at a slow rate, the clutch'elements 12 and 13 are engaged (see Figure 5) by downward movement of the control handle 52, as indicated above. Note that this permits the rod '94 to be lowered, and this lowering movement, by means not shown, but knownin'the art, effects outward projection of the tool 92 to the diameter of the cylinder to be'cut. With the clutch elements 12 and I3engaged, rotation of the shaft 96 through. the key 19 rotates the driving gear 1, which inv turn rotates the idler gear 1|, and this rotates the gear 70. In turn the sleeve 14 is rotated by the engagement of the clutch elements 12 and 13, and the sleeve 14, being keyed to the nut 16, rotates the latter, but since the gears 1 and 10 contain a different number of teeth, they Will rotate at a slightly differential rate, so that while the shaft 96'and the nut 16 both rotate, their rate of rotation will be different, and the combination will effect downward feed of'the boringbar at a slow rate. 9| is being rotated, since the gear I driven from the driving gear I, is secured to the hollow shaft 1|, passing through the axial boreof the boring head 9, and carrying the cutter head 9| at its lower end. v

When it is desired to movethe boring :bar upwardly, the slidable clutch elements 63 are shifted, as described above, into their lower position (compare Figures 2 and 6) to engage the complemental clutch elements 62; This necessarily disengages clutch elements 13 and I2, and increases the rate of rotation of the sleeve 14 and consequently of the nut 16 keyed thereto, by reason of the difference in size of gears and 6, and since the screw 96 continues to rotate at the same rate, this will effect upward movement of the boring bar at a rapid rate.

If it is desired to effect more rapid downward movement of the boring bar, as, for example, when" using the centering fingers 93 to preliminarily align the axis of the boring bar withtheaxis of the cylinder, this may be accomplished by stopping rotation of the sleeve 14 and nut 16. This is readily accomplishedby pressing inward the button 8, against its spring 8|, whereby-its inner end 82 engages one of several notches 11 in the exterior of the sleeve 14. The nut 13 being thus held stationary, but the screw 96 continuing to rotate, the head 91 and-the boring bar are moved downward rapidly. As will be evident from inspection of Figure 5, engagement of .pin 82 in a notch 11 can only occur when sleeve 14' is in a neutral position, at which time neither clutch 13 12, or 63, 62 is in engagement. Since Meantime the cutter head the pin 82'wil1 only remain in engagement with 1.1 so long as itispressed inward against the spring 8|, it is'assured that the operator will stand by, to prevent rapid downward feed to progress further than, is desired. e

It will be seen. from the above that theseveral clutch elements are so interconnected. and arranged that there can not be engagement of any two sets of clutch elements at anyone time. The base 90 is provided with a-boss 90' and a set screw 90". (see Figure 1), in which is received a vertical rod 3. This rod, which is held by the bore toextend parallel to the axis of the boring bar 9, extends vertically upward, and its upper end is axially bored, as indicatedlin Figure 5, to receive a compressible spring 3|],-v holding upwardly a headed plunger 3|. Also formed on the upper end of the rod 3 is a cam surface, in the shape of a cone 32. The plunger-3| is positioned in the path of movement of the control handle 52,, so that as the latter, moving with the head 91, approaches the. desired lower limit of its movement, at which time the cutting tool 92 will have passed beyond the lower end of the cylinder which it is'reboring, the plunger will have been depressed by vprevious contact with the control handle 52, and the spring 30 will have been compressed. If the control handle 52 had been there- 'tofo-re latched or held in its downward position, to

accomplish downward feed of the boring bar, but is ,now unlatched or released, this compression of the spring 30, acting ,through theplunger 3|, will throwthe control handle 52 upwardly into position to engage the clutch elements 63 and 62, thereby initiatingupward movement of the boring bar.

In order to control the point of this reversal I provide latching means to hold the control handle 52 ,either in its downward position or in its upward position). Such latching means, best shown -in Figure '1, may comprise a square-headed stud 2 fixed in the casing 91, anda latch 2|] formed as part of a lever 2| pivoted at 22 upon the outer end of the control handle 52. A spring 23 tends to hold the latch 20 in engagement with the stud 2. .The lever 2| carries a finger 24 atits lower end, which will engage the cam or conical surface 32 upon compression of, thespring 30 to a-desired extent, and the lever 2| will thereby be rocked to an extent to disengage the latch 20 from the stud 2, so that upon apredetermined amount of compression of the spring the'latchlng means will be disengaged, to throw the control handle 52 into its upper position, corresponding to upward feed of the boring bar, whereuponthe latch 20 will engage the upper side of the stud 2, being pressed inward by the spring 23, and upward movement of the boring bar will be effected. It

will'be seen that. the-point of disengagement and reversal may becontrolled by adjustment of the rod 30 vertically in its, boss 90, and that it may be held in any adjusted position by the set screw Upon reaching the upper limit of movement of the boring bar a second finger 25 (see Figure 5) on the lever 2 I, positioned to engage beneath the head 96 on the screw 96, comes into engagement with the head 96, again rocking the lever 2| and disengaging the latch2|| from the stud 2, permitting the control handle 52 to drop to its neutral position, where it is heldby-a spring 59 (see Figure 7). v

-'-To control ,movementzof the handle 52 a finger button 26 may be provided on the lever 2|, which maybe pressed upwardly-or downwardly to accomplish corresponding movement of theboring' bar, it being remembered that downward mo've-. ment of the control handle 52 engages slow down feed clutch elements 13 and 12, and upward movement of the control handle engages fast up feed clutch elements 63 and 62. Another finger button 21 may be provided on the lever 2|, which when pressed or struck will always (as in an emergency) disengage the latch 20 from'the, stud2, and permit the control handle 52 to return to its neutral position, stopping all feed of the boring bar. 1

The rotative screw head 96 may be employed as a, grinding and lapping tool, as disclosed in my companion, application, Serial No. 70,858, referred to above. In' so doing the tool bit is held in a-jig secured to the casing 91, and no variation in the vertical position of the head 96' relative to the casing 91 can be permitted. Using a lefthanded thread, turning in the direction of the arrow A (Figure 5), as in my Patent No. 2,011,815, I dis covered that there was a tendency with the sleeve 14 in neutral position, for the casing 91 to move upwardly, then downwardly, with considerable fluctuation in load on the motor, indicating recurring friction in the machine. The upward speed as the screw, the casing would drop, and

the upward movement would recur.

Merely to provide an antifriction bearing, as at 98, was found not to avoid this tendency, hence, by reversal of the direction of the screw threads (making it right-handed instead of left-handed), continuing the same direction of rotation of the screw, and making the differential gear 1|) with one (or'more) tooth more than the driving gear 1, I found that the tendency for the nut 15 to climb up the screw while in neutral was converted into a tendency for it to move downward on the screw. While this might be considered immaterialits immovability with respect to the screw being the desideratum-it will be observed that any tendency for the nut to move down wardly will only result in a pressure of the nut on the extension 1 of the gear 1. Since the latter is keyed to the screw and must rotate therewith, and as any pressure of the nut upon the gear 1 will tend to cause the two to rotate at the same speed, it follows that any such pressure only brings about the very result desired, without any friction. The motor load is therefore steady and light, and the objectionable up and down movement of the casing 91 is completely overcome by this change.

Upwardthrust from the nut to the casing 91, such as occurs during upward feed of the boring bar, with the nut rotating in the same direction as and more rapidly than the screw, is taken by the antifriction bearing 98, and as themotor is free at such times from any other load, this is unobjectionable. I have found that the present arrangement lessens the load on the motor during slow downward feed, when the fiy cutter 92 is operating, in comparison to its load under the lll 'and the nut 16, around,by-this-frictional action relieving the gearing ofa' large part of its load, and lessening the friction of-the whole. It has been observed that this result occurs, and this lessens wear and the motor load, hence lengthens the life and reliabilityfof the entire boring bar. With the arrangement of my prior patent the differential gear and rint, rotating more rapidly than the main driving gear and screw, and about a screw which was left-handed, tended to wedge the nut more tightly between the incline of the screw thread and the driving gear, thus producing more friction than in the present arrangement, hence a greater load on the motor at a time when its maximum load was imposed. I

What I claim as my invention is:

1. In a reboring machine, in combination with a base, a boring bar vertically/reciprocable in the base, and terminating at'its upper-endi'n a head constituting agear casing, a power-driven screw journaled in the base and extending through the head,'a nut threaded thereon, two differential gears, one constituting a driving gear and keyed to the screw, and the other loose thereon, a common gear in mesh with each differential gear, a gear-toothed sleeve slidable along and keyed to rotate with the nut, a set of comp-lemental clutch elements, one part on theloose gear and one part on the sleeve, engageable by downwardmovement of said slidable sleeve to' advance theboring'bar slowly downward, a pair'ofgears' of unequal diameter in mesh respectively with the driving gear and the sleeves gear teeth, a second set of complemental clutch elements on the unequal gears engageable when said sleeve is shifted upwardly, to rotate the nut at a different speed and in a difierent direction relative to the screw, thereby to eifect upward movement of the boring-bar, a control handle shiftableupwardly or downwardly from a neutral position to control upward or downward shifting of the sleeve, and thereby the engagement of the respective clutch elements, a third set of clutch elements,-'one' part formed on the sleeve, the other partbeing fixedly positioned, the two parts being engageable to stoprotation of the nut, and to eflfe'ct rapid downward movement of the boring bar," the last-mentioned clutch elements on the sleeve being disposed,relative to the fixedly positioned clutch element, to be engaged only when the sleeve and its otherclutch elements are in neutralposition, thereby to interdict engagement of the last'set of clutch elements except whenthe'other' twosets of clutch elements are in neutral position.

2. In a reboring machine, in combination with abase; a boring bar vertically reciprocable in said base, power feed mechanism operatively connected to the boring bar to effectsuchreciprocation including a continuously rotating driving gear, a clutch sleeve operatively connected at all times to thefeed mechanism for rotation" therewith, and movable to and from clutch-engaged position, means operable to efiect downward feed of the boring bar when'the clutch sleeve'is in such position, a gear formed'on said clutch sleeve, of a diameter difi'erent from that of the driving gear, twodifferently sized, axially aligned gears meshing with the driving gear and with the clutch sleeve gear, respectively; cooperating clutch elements to connect said aligned'gears, yieldable means normally holding said clutch ele 'ments disengaged, means operable by such'engagement ofthe said clutch elements to effect upward feed of the. boring bar, and control means commonto ithe'clutch'sleeve and to the cooperating" clutch elements, movable in one direction from'a neutral'position to place the :clutch sleeve in" clutch en'gaged position for downward feed, and. movable in the opposite direction from such neutral :position to engage the cooperating clutch elements, *thereby to effect upward feed of the boringban'. M w

3. In a'reboring machine, in combination with a base, a boring bar Verticallyreciprocable in said base, a power driven screw parallel to the boring bar, a'driving gear carried by the boring bar and keyed-to and. movable axially along said screw, a differential gearvcoaxial with the'driving gear and having a greater number of teeth, an idler gear meshing with the driving and differential gears, whereby the former gains on the latter, a nut'threaded on said screw, a clutch sleeve slidalole on and connected to rotate with said nut, cooperative clutchelements formed on the clutch sleeve and diiferential gear, the screw having such direction of thread and rotating in such direction that, when said clutch elements are engaged, the nut feeds the boring bar slowly downward, gear teeth formed on'the clutch sleeve, of less diameter than the driving gear,'a pair of unequal coaxial gears, the smaller one meshing with the driving gear and the larger one with the sleeve gear, cooperating clutch elements to connect said pair of gears, whereby, when they are engaged, to rotate the nut relatively to the screw in a direction to feed the boring bar rapidly upward, and selective means movable from a neutral position-to engagethe clutch sleeve with the differential gear or alternatively to eng'age the two aligned gears, thereby to control the direction of feed of the boring bar.

4. In a reboring machine, in combination" with a base,'a boring bar vertically reciprocable in the base, power means for'efiecting such reciprocation, includinga drive shaft and a clutch gear shiftab'le to effect slow feed downward, a second clutch'gear"meshed'with said first clutch gear and shiftable' to effect upward feed, drive means connecting each of said clutch gears,"-in clutch- A engaged position, with said drive shaft, and a ro'ck shaft'interengaged between said two clutch gears, and oscillatable'in one direction to move said downward feed clutch gear from a neutral position, wherein neither clutch gear is operative, into-bar driving position, said upward feed clutch gear remaining in neutral position, and oscillatable in the opposite direction to move conjointly and simultaneously said downward feed'clut'ch gear into neutral position and said upward feed clutch gear into bar driving position.

5; In a reboring machine, in combination with a base, a boring bar vertically reciprocable in the base,and having a nonrotatable head, power means including two rotatable clutch elements, a control element shiftable from a neutral position into 'either' of two clutch-engaged positions for rotation by one or the other of said clutch elements, thus to effect 'either slow downward feed or upward feed of the boring bar, and a locking tral' position, to hold said control member from rotation, thus to effect rapid downward ment of the head. 7

' 6. In a reboring machine, in combination with movea base, a'boring bar vertically reciprocable'in the base, power means. for efiecting such reciprocation, including a clutch gear shiftable to ,eifectlow' speed downward, a second clutch gear meshed with said-first'clutch gear and shiftable to effect upward feed, a rock'shaftinterengaged between said two clutch gears, and oscillatable in one direction to move said downward feed 1 clutch gear from a neutral position into bar driving position, and oscillatable in the opposite .direction to move simultaneously said downward feed clutch gear into neutral position and said upward feed clutch gear into bar driving position, and means engageable by relative movement transversely of one of the aforementioned clutch gears, only when both are in neutral position, to control them for effecting rapiddownward'movement of the boring bar.

'7 In a'reboring machine, in combination with a base, a boring bar vertically reciprocable in the base, and carrying a head constituting a gear casing upon its upper end, power means for effecting such reciprocation including a threaded shaft extending through said head, parallel to the boring bar, a nut threaded on said shaft, a driving gear keyed to the shaft, a differential gear loose on the shaft, and a common gear I meshing with both said gears, and means to clutch the differential gear to the nut to effect differential rotation of the nut and threaded shaft, said clutch means being movable into neutral position, the driving gear having an extension engageable with the nut, the parts being so arranged, rotated, and disposed that in such neutral position the nut abuts said extension, which rotates with the shaft, on the side thereof toward which the nut tends to travel along the screw when held from rotation therewith, retardation in the nuts rotation thus tending to jam the nut against said element, whereby the nut increasingly tends to rotate at precisely the same speed as the threaded shaft.

8. In a reboring machine, in combination with a base, a' boring bar vertically reciprocable in the base, and carrying a head constituting a gear casing upon its upper end, a threaded shaft extending through the said head and rotatable to effect reciprocation of the boring bar, a nut threaded on said shaft, and movable forward therealong as the shaft rotates while the nut is held from rotation or rotates at a speed slower than said shaft, a member keyed to rotate with said shaft and frictionally abutting the forward side of said nut, tending normally to increase its speed of rotation to equal that of said shaft as the nut moves forward along the bar to press against said member, thus to check the forward movement of the nut, and means operable at will to effect positive relative rotation of the screw and nut to move said nut and said keyed member along the screw, thus to reciprocate the boring bar.

9. In a reboring machine, in combination with a base, a boring bar verticallyreciprocable in the base, and carrying a head constituting a gear casing upon its upper end, a right-hand threaded vertical shaft journaled in the base and extending through the head, a nut threaded on said shaft, power means to rotate said shaft in a direction to move said nut downward along the shaft when the nut is held from rotation or rotates at a speed slower than said shaft, a driving gear keyed upon and rotating with said shaft, and disposed immediately below and frictionally abutting said nut, tending normally to rotate the nut therewith at the same speed as said shaft, and means interconnectable between said driving gear and said nut to effect rotation of the nut at a slower speed than said shaft and driving gear,

journaled in the base and extending through the head, a nut threaded thereon, two differential gears, one constituting a driving gear and keyed to the screw, and the other loose thereon, a common gear in mesh with each differential gear, a

gear-toothed sleeve slidable along and keyed to rotate with the nut, a set of complemental clutch elements, one part on the loose gear and one part on the sleeve, engageable by lengthwise movem'ent of the sleeve in one direction to ad- Vance the boring bar in a downward direction,

a pair of unequal gears meshing respectively with the driving gear and with the sleeves gear teeth, a second set of complemental clutch elements movable to connect or to disconnect the unequal gears, whereby to rotate the nut in a different direction relative to the screw, when the latter clutch elements are connected, and to effect advance of the boring bar in the opposite direction, and means controlling the engagement of the two sets of clutch elements, to interdict engagement of either set while the other set is engaged.

11. In a reboring machine, in combination with a base, a boring bar vertically reciprocable in the base, and terminating at its upper end in a head constituting a gear casing, a power-driven screw journaled in the base and extending through the head, a nut threaded thereon, two differential gears, one constituting a driving gear and keyed to the screw, and the other loose thereon, a common gear in mesh with each differential gear, a gear-toothed sleeve slidable along and keyed to rotate with the nut, a set of complemental clutch elements, one part on the loose gear and one part on the sleeve, engageable by lengthwise movement of the sleeve in one direction to advance the boring bar in a downward direction, a pair of unequal gears meshing respectively with the driving gear and with the sleeves gear teeth, a second set of complemental clutch elements movable to connect or to disconnect the unequal gears, whereby to rotate the nut in a different direction relative to the screw, when the latter clutch elements are connected, and to effect advance of the boring bar in the opposite direction, means controlling the engagement of the two sets of clutch elements, to interdict engagement of either set while the other set is engaged, and a third set of clutch elements, one part formed on the sleeve and the other part being fixedly positioned, and when engaged stopping rotation of the nut, to effect rapid feeding movement of the boring bar, the last-mentioned clutch elements on the sleeve being disposed, relative to the other two sets of clutch elements and the means controlling the same, to be engaged only when the other two sets of clutch elements are in neutral position.-

12. In a reboring machine, in combination with a base, a boring bar vertically reciprocable in the base, and terminating at its upper end in a head constituting a gear casing, a power driven screw journaled in the base and extending through the head, a nut threaded thereon and held in said head, three sets of clutch elements, each set including one part operatively connected to the nut to rotate therewith, and a complemental part engageable with its first part, means operable by engagement of one such set of clutch elements to efiect slow relative upward feed of thenut along the screw, thereby-to efiect slow downward feed of the boring bar, means operable by engagement .of a second such-set of clutch elements to effect ing bar.

13. The combination of claim 12, including also means controlling the engagement of the several sets of clutch elements, and interdicting engagement of any other set while any given set is in engagement.

14. In a reboring machine, in combination with a base, a boring bar vertically reciprocable in the base, and carrying a head constituting a gear casing uponlits upper end,1a threaded vertical shaft tjournaled'intthe' base and extending through the head; a .nutthreaded on said shaft,v power means :t-o.rotate said shaft-in a direction to move said =nut downward along the shaft when the nut is held from rotation or rotates in the same direction at a speed-slower than said shaft, a member constituting part of said power means keyed upon and-rotating with said shaft, and disposed immediately beneath and frictionally abutting said, nut, tending normally tov jam against the nut for rotation of the two jammed-together elements at-precisely the same speed and in the'same direction as the shaft, and clutch means interconnectable between said power means and the nut to effect rotation of the nut at a slower speed than said shaft and said keyed member, thus to efiect movement-of said keyed member along said shaft by pressure of the nut thereagainst.

CLARENCE T. ROTTLER. 

